Recombinant viruses represent powerful tools that could serve as new vectors for vaccination against bioterrorism agents such as Yersinia pestis. Using a well-developed mouse model system, our recent published work has shown that the paramyxovirus SV5 has inherent properties that could be exploited to create novel vaccine vectors expressing Y. pestis subunits. However, vaccines that are based on subunits from bioterrorism agents are usually not highly immunogenic by themselves. The recent discovery that activation of cellular toll-like receptors (TLRs) can have major effects on adaptive immunity raises the exciting possibility that TLR agonists could be engineered as adjuvants to enhance responses to subunit vaccines for bioterrorism agents. We will test this hypothesis by designing rSV5 vectors that express the Y. pestis V antigen with or without co-expression of TLR agonists. In the first aim, we will identify rSV5 vectors that have an optimal co-expression of Y. pestis V antigen and polypeptide agonists that have been shown previously to activate either TLR2 or TLR4 signaling pathways. The ability of rSV5-derived TLR agonists to activate and to tolerize TLR signaling pathways will be assessed in tissue culture cells. Mice infected intranasally with rSV5 vectors coexpressing V antigen and TLR agonists will be analyzed for the degree of inflammation in the respiratory tract using histopathological assessment, assays for cytokine expression and quantitation of cellular infiltration. In the second aim, we will test the hypothesis that co-expressing TLR agonists will enhance the antibody response against the Y. pestis V antigen. Anti-V antibody responses will be determined in mice infected intranasally with rSV5 vectors expressing V antigen alone or in combination with TLR agonists. We will seek to identify the rSV5-pestisV-TLRag vectors that have an optimal balance between enhanced anti-V responses (aim 2) and minimal lung inflammation (aim 1). There is a growing interest in the use of newly-discovered TLR agonists as potent adjuvants. At the conclusion of these studies, we will have tested the hypothesis that delivery of TLR agonists from a noncytopathic viral vector can enhance antibody responses. A powerful new class of viral vectors will be available for enhancing the immune response to an important bioterrorism agent. We will then be in an excellent position to test these rSV5 vectors in an available mouse model system for their ability to confer protection from Y. pestis challenge.